The major task of pharmacological research is to develop drugs having highly selective therapeutic actions but with limited adverse side effects. Increasingly, the insights and approaches provided by modern cell and molecular biology are being applied to problems of drug development. No where is this more appropriate than in the field of controlled or "targeted" drug delivery. In recent years it has become clear that enhanced therapeutic actions can often be attained by manipulating the kinetic behavior, tissue distribution and cellular interactions of therapeutic agents. In the past, physical and engineering-type approaches have been quite successful in the development of controlled drug delivery systems. More recently, biological molecules including immunoglobulins, other proteins or peptides and even oligonucleotides, have been used either as carriers for drug molecules or as therapeutic entities themselves. The aim of this conference is to develop a "cutting edge" synthesis of the available information on the factors which control the in vivo distribution of complex molecules such as proteins and to assess how this information may be applied to the design of therapeutic agents. The conference will bring together cell and molecular biologists who have insights into the signals and processes which regulate the movement of macromolecules across membrane barriers, with pharmacologists, medicinal chemists and pharmaceutics experts having knowledge of drug development and interests in the problem of drug delivery. This should provide a unique and valuable opportunity to chart the recent history and likely further evolution of biological approaches to drug targeting.